1. Field of the Invention
The present invention relates to a key touch data generation circuit in an electronic musical instrument and, more particularly, to a key touch data generation circuit suitably applied to a circuit for measuring a key depression speed using a counter.
2. Description of the Background Art
In an electronic musical instrument having a plurality of keys, touch data are obtained in units of keys, and the amplitude envelope, or the like of an output waveform of a digital tone source is controlled. The touch data is obtained in such a manner that two key switch contacts corresponding to different key depression depths are arranged for each key, and an operation time difference between the two key switch contacts is measured. The operation time difference is measured by a counter for counting clock pulses of a predetermined frequency.
Counters for detecting key touch data are normally arranged in one-to-one correspondence with keys. On the other hand, in some polyphonic electronic musical instruments, the number of simultaneous (parallel) tone generation channels of a digital tone source is considerably smaller than the total number of keys. In such an electronic musical instrument, the number of counters for detecting key touch data is smaller than the total number of keys (e.g., Japanese Patent Publication No. 64-8356).
In the electronic musical instrument in which the number of counters for detecting key touch data is small, key touch data cannot be generated if keys exceeding the number of counters are simultaneously depressed.